Added: support for dhcp.leases file (for aliases)

You can now provide a normal dhcp.leases generated by dnsmasq
with -l/--leases.

Example:

  ./bat2nodes.py -m bat0 -l /tmp/dhcp.leases -d ../ffmap-d3
Added: Argument -n/--norrd to skip rrd database creation/update process
Added: ssh proxy command support

In case your ffmap-backend server is not part of the mesh you can use
ssh to tunnel to your batman mesh.

Example:

  bat2nodes.py -m bat0 -s root@10.0.0.1 -d ../ffmap-d3
Refactoring: Removed duplicated code